# std::ranges::make_heap

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< cpp‎ | algorithm‎ | ranges

Defined in header `<algorithm>` |  |
Call signature |  |
template< std::random_access_iterator I, std::sentinel_for<I> S, class Comp = ranges::less, class Proj = std::identity > requires std::sortable<I, Comp, Proj> constexpr I make_heap( I first, S last, Comp comp = {}, Proj proj = {} ); | (1) | (since C++20)
template< ranges::random_access_range R, class Comp = ranges::less, class Proj = std::identity > requires std::sortable<ranges::iterator_t<R>, Comp, Proj> constexpr ranges::borrowed_iterator_t<R> make_heap( R&& r, Comp comp = {}, Proj proj = {} ); | (2) | (since C++20)

Constructs a heap with respect to comp and proj from the elements in the specified range.

1) The specified range is `[`first`,` last`)`.
2) The specified range is r.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

### Parameters

first, last | - | the iterator and sentinel designating the range of elements to modify
r | - | the range of elements to modify
comp | - | comparator to apply to the projected elements
proj | - | projection to apply to the elements

### Return value

1) last
2) ranges::end(r)

### Complexity

At most \(\scriptsize 3\cdot N\)3·N applications of comp and \(\scriptsize 6\cdot N\)6·N applications of proj, where \(\scriptsize N \)N is:

1) ranges::distance(first, last)
2) ranges::distance(r)

### Example

Run this code

    #include <algorithm>
    #include <cmath>
    #include <functional>
    #include <iostream>
    #include <vector>

    void out(const auto& what, int n = 1)
    {
        while (n-- > 0)
            std::cout << what;
    }

    void print(auto rem, const auto& v)
    {
        out(rem);
        for (auto e : v)
            out(e), out(' ');
        out('\n');
    }

    void draw_heap(const auto& v)
    {
        auto bails = [](int n, int w)
        {
            auto b = [](int w) { out("┌"), out("─", w), out("┴"), out("─", w), out("┐"); };
            if (!(n /= 2))
                return;
            for (out(' ', w); n-- > 0;)
                b(w), out(' ', w + w + 1);
            out('\n');
        };

        auto data = [](int n, int w, auto& first, auto last)
        {
            for (out(' ', w); n-- > 0 && first != last; ++first)
                out(*first), out(' ', w + w + 1);
            out('\n');
        };

        auto tier = [&](int t, int m, auto& first, auto last)
        {
            const int n{1 << t};
            const int w{(1 << (m - t - 1)) - 1};
            bails(n, w), data(n, w, first, last);
        };

        const int m{static_cast<int>(std::ceil(std::log2(1 + v.size())))};
        auto first{v.cbegin()};
        for (int i{}; i != m; ++i)
            tier(i, m, first, v.cend());
    }

    int main()
    {
        std::vector h{1, 6, 1, 8, 0, 3, 3, 9, 8, 8, 7, 4, 9, 8, 9};
        print("source: ", h);

        std::ranges::make_heap(h);
        print("\n" "max-heap: ", h);
        draw_heap(h);

        std::ranges::make_heap(h, std::greater{});
        print("\n" "min-heap: ", h);
        draw_heap(h);
    }

Output:

    source: 1 6 1 8 0 3 3 9 8 8 7 4 9 8 9

    max-heap: 9 8 9 8 8 4 9 6 1 0 7 1 3 8 3
           9
       ┌───┴───┐
       8       9
     ┌─┴─┐   ┌─┴─┐
     8   8   4   9
    ┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐
    6 1 0 7 1 3 8 3

    min-heap: 0 1 1 8 6 3 3 9 8 8 7 4 9 8 9
           0
       ┌───┴───┐
       1       1
     ┌─┴─┐   ┌─┴─┐
     8   6   3   3
    ┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐
    9 8 8 7 4 9 8 9

### See also

ranges::is_heap (C++20) | checks if the given range is a max heap (algorithm function object)
ranges::is_heap_until (C++20) | finds the largest subrange that is a max heap (algorithm function object)
ranges::push_heap (C++20) | adds an element to a max heap (algorithm function object)
ranges::pop_heap (C++20) | removes the largest element from a max heap (algorithm function object)
ranges::sort_heap (C++20) | turns a max heap into a range of elements sorted in ascending order (algorithm function object)
make_heap | creates a max heap out of a range of elements (function template)

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